WO2009144499A2

WO2009144499A2 - Smoking article filter ventilation

Info

Publication number: WO2009144499A2
Application number: PCT/GB2009/050576
Authority: WO
Inventors: Richard Fiebelkorn; Glen Elgar
Original assignee: British American Tobacco (Investments) Limited
Priority date: 2008-05-30
Filing date: 2009-05-28
Publication date: 2009-12-03
Also published as: WO2009144499A3; AR074038A1; CL2009001291A1; GB0809857D0; TW201016150A

Abstract

A filter for a smoking article such as a cigarette comprises a core, a wrapper surrounding the core, and at least one ventilation hole extending though the wrapper into the core to a depth such that air drawn in through the ventilation hole enters a central region of the core. The ventilation holes may be configured so that air preferentially enters the central region compared to the periphery of the core, and may have a depth in the range 2 - 3.5 mm.

Description

SMOKING ARTICLE FILTER VENTILATION

BACKGROUND OF THE INVENTION

The present invention relates to ventilation holes in filters for smoking articles.

Prefabricated smoking articles that comprise a tobacco rod attached to a filter, such as cigarettes and superslim cigarettes, often include ventilation holes in the filter. The purpose of the holes is to allow air to enter the filter when a smoker draws on the cigarette. The air mixes with the smoke and other components drawn through the filter from the ignited tobacco and provides dilution. The holes are typically arranged as a row or zone around the circumference of the filter, approximately 11 to 16 mm from the mouth end of the filter. There are a range of techniques currently used for making ventilation holes.

The tipping paper, which is wrapped around the cigarette to join the tobacco rod to the filter, may be pre-perforated before wrapping by a mechanical or electrostatic perforating device or by a laser beam. Alternatively, a laser beam may be used to make the holes after the cigarette is assembled, using an on-line or on-machine-line system. In the latter case, the holes are burnt into the filter by the focused laser beam, and hence pass through the paper or papers wrapped around the filter (tipping paper, wrapping paper) and into the acetate tow from which the filter core is made, to a depth of a millimetre or two. In all cases, the result is to allow the diluting air to be drawn into the outside regions of the filter. This in turn causes the main smoke flow to be concentrated into the centre of the filter, in some cases leading to unsightly staining at the mouth end of the filter.

The location of the holes along the filter length can modify the filtering and dilution effects, in particular if the holes are positioned with reference to individual components of a multi-segment filter, or if the filter has an annular construction or has an annular component such as a peripheral layer of adsorbent material.

It is therefore advantageous with certain types of filter design for the smoke to be channeled away from the centre to a position close to or at the periphery of the filter.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a filter is provided for use in conjunction with a smoking article, the filter comprising a core, a wrapper surrounding the core, and at least one ventilation hole extending though the wrapper into the core to a depth such that air drawn in through the ventilation hole enters a central region of the core.

The ventilation hole may be configured such that air drawn in through the ventilation hole preferentially enters the central region of the core.

The ventilation hole may be defined by a surface that is more permeable to air in the central region of the core than in a peripheral region of the core.

The ventilation hole may have a depth of at least 2 mm, preferably 2 - 3.5 mm.

The ventilation hole may have a depth that is at least 25% of the diameter of the filter, preferably 25 - 50 % of the diameter of the filter.

The filter may comprise a plurality of the said ventilation holes, which may be arranged in at least one circumferential row or zone around the filter.

The filter may be a multi-segment filter such that the core comprises two or more segments disposed longitudinally along the filter. The filter may be an annular filter such that at least part of the core comprises a central portion surrounded by an annular portion, and the filter may further comprise a flavour thread disposed longitudinally in the central region of the core.

The wrapper may be permeable to at least one gas carried by smoke from burning tobacco, and may be permeable to carbon monoxide. The ventilation hole or holes may be made using a laser beam.

According to a second aspect of the present invention, a smoking article is provided comprising a filter as described above.

According to a third aspect of the present invention, a method is provided for manufacturing a filter for use in conjunction with a smoking article. The filter comprises a core and a wrapper surrounding the core, and the method may include manufacturing at least one ventilation hole which extends though the wrapper into the core to a depth such that air drawn in through the ventilation hole enters a central region of the core. The method may include configuring the ventilation hole such that air drawn in through the ventilation hole preferentially enters the central region of the core.

The method may include configuring the surface of the ventilation hole such that the surface is more permeable to air in the central region of the core than in a peripheral region of the core. The method may include configuring the ventilation hole to have a depth of at least 2 mm, preferably 2 - 3.5 mm.

The method may include configuring the ventilation hole to have a depth that is at least 25% of the diameter of the filter, preferably 25 - 50 % of the diameter of the filter. The method may include generating a plurality of the said ventilation holes, which may be arranged in at least one circumferential row or zone around the filter.

The method may include configuring the filter in the form of a multi-segment filter such that the core comprises two or more segments disposed longitudinally along the filter. The method may include configuring the filter in the form of an annular filter such that at least part of the core comprises a central portion surrounded by an annular portion.

The method may include configuring the filter to comprise a flavour thread disposed longitudinally in the central region of the core. The method may involve the use of a wrapper is permeable to at least one gas carried by smoke from burning tobacco, and the smoke may be carbon monoxide.

The method may include using a laser beam to manufacture the ventilation hole or holes, and the method may include operating the laser in situ on a machine for manufacturing the smoking articles provided with the filter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same may be carried into effect reference is now made by way of example to the accompanying drawings in which:

Figures IA and IB show cross-sectional views through cigarettes comprising shallow ventilation holes according to the prior art;

Figure 1C is a photograph showing the staining pattern on the end of the filter of a smoked cigarette comprising shallow ventilation holes according to the prior art;

Figure 2 A shows a cross-sectional view of a cigarette comprising deep ventilation holes according to an embodiment of the present invention

Figure 2B shows a cross-sectional view of a cigarette comprising deep ventilation holes according to a further embodiment of the present invention; Figure 2C is a photograph showing the staining pattern on the end of the filter of the cigarette of Figure 2B after smoking;

Figure 2D is a photograph showing a cross sectional view of a filter tip comprising deep ventilation holes;

DETAILED DESCRIPTION

Known ventilation holes in smoking article filters are formed only in the tipping paper as pre-perforations, or are made using a laser beam to burn shallow holes into an assembled smoking article or smoking article filter, through the paper and into the outer regions of the core of the filter.

Figure IA shows a longitudinal cross-sectional view through a cigarette of simple construction that has pre-perf orated ventilation holes. The cigarette 10 comprises a tobacco rod 12 joined to a filter 14 by a tipping paper 16 stuck around the cigarette 10 over the join between the rod 12 and the filter 14. The tipping paper 16 has a row of ventilation holes 18 that extend around the circumference of the filter 14.

The tobacco rod 12 comprises tobacco wrapped in a paper wrapper 19. The filter 14 comprises a filter core 20 made from acetate tow wrapped in a filter wrapper 22. The wrapper is sufficiently gas permeable that air drawn in through the holes 18 can pass through the wrapper 22 and into the core 20.

Figure IB shows a longitudinal cross-sectional view through a cigarette having on-machine laser-formed ventilation holes. The cigarette 24 comprises the same components as the cigarette 10 of Figure IA, with the exception that the ventilation holes 18, having been burnt by a focused laser beam, extend through the tipping paper

16, the underlying filter wrapper 22 and a short distance into the filter core 20.

Typically, holes made by laser have a depth of the order of 1 to 2 mm.

In each case, the flow of air through the filter 14 when a smoker draws on the lit cigarette is similar. The positioning of the holes 18 in the surface region of the filter 14 is such that the air enters the filter 14 and flows along the outer, peripheral region of the core 20, where it dilutes the smoke travelling through the filter 14 from the burning tobacco rod 12. In Figures IA and IB the air flow is indicated by the small arrows 26 and the smoke flow is indicated by the large arrows 28.

This peripheral air flow is evident from observations of the end of the filter of a smoked cigarette, where the central region is stained by deposits of materials carried by the smoke that have been trapped by the filter, and the periphery, through which the more diluted smoke has passed, is much less stained. Figure 1C shows a photograph of the end of such a filter 14, with the core 20 having staining in a central region 30 and little staining in the surrounding peripheral region 32.

In contrast, the present invention proposes providing a filter that has deep ventilation holes, extending a significant depth into the core of the filter. In this way, air flow can be modified compared with flow in a filter with conventional ventilation holes, providing different dilution effects. Deep ventilation holes allow air drawn in through the ventilation holes to reach the central region of the core, so that smoke propagating along the core centre can be diluted. Figure 2A shows a longitudinal cross-section through a first example of a cigarette having a filter with deep ventilation holes. The cigarette 34 has the same construction as that shown in Figure IB, except that the ventilation holes penetrate deep into the core 20 of the filter 14. Assuming that the walls of the holes (the core material that forms the hole boundaries within the core) are roughly uniform with regard to air permeability, air drawn in through the holes can enter the core over the depth of the hole, and flow longitudinally through much of the volume of the core downstream from the ventilation holes. The arrows 26 in Figure 2A illustrate this. Smoke dilution is thereby much more uniform than for the surface ventilation in conventional filters, with smoke being diluted in both the core region and the peripheral region.

Figure 2B shows a longitudinal cross-section through a second example of a cigarette including deep ventilation holes. The cigarette 36 is substantially the same as that shown in Figure 2 A, with a row of deep ventilation holes 18 around the circumference of the filter 14. In this example, however, the air permeability is not uniform in the walls of the holes. Instead, the permeability is greater towards the bottom of the holes, i.e. greater in the core region of the filter than in the peripheral region. The effect of this is that air drawn in through the ventilation holes preferentially enters the core region as compared to the outer region, as shown by the arrows 26. Hence, the smoke 28 is diluted much more in the core region. Figure 2C shows a photograph of an end view of a filter 14 of a smoked cigarette having deep ventilation holes that give preferential air flow in the centre of the filter. The staining caused by materials in the smoke trapped by the filter has the opposite appearance to that in a cigarette with conventional shallow holes, in that the staining is greater in the peripheral region 32 of the filter core than in the central region 30.

Figure 2D shows a photograph of a cross section of a filter 14 having the deep ventilation holes. The deep ventilation holes 18 can be seen to penetrate substantially into the core 20 of the filter 14. There are a number of advantages of deep ventilation holes in general and further of providing air dilution of smoke preferentially in the central region of the filter:

Filtration efficiencies can be modified by selection of an appropriate depth of hole. - A greater range of filtration possibilities is made available if deep holes are combined with multi-segment filters.

More efficient use can be made of annular filter configurations, for example the use of adsorbent material round the periphery of the filter will enhance the removal of unwanted vapour phase components from the smoke. The consistency of the ventilation level is improved, since any errors in the hole depth are a smaller percentage error than for shallow holes made using the same equipment. Thus, variability between individual holes and between cigarettes is reduced. Smoke bleed from the ventilation holes is reduced. - Changes in the ventilation level as the air and smoke flows change during the course of the cigarette being smoked are reduced. The concentration of the smoke flow in the peripheral region can be used in combination with porous or gas-permeable tipping and wrapping papers to enable greater diffusion of undesirable gases (such as carbon monoxide) out of the filter.

Air dilution in the centre means that the more undiluted smoke passes through the outer region of the filter, which can have a larger volume than the central region (depending on the depth of the deep ventilation holes) so that better filtration can occur. A related point is that the same amount of filtered material is deposited in a larger volume of filter so that the intensity of the staining is less, improving the appearance of the filter during and after smoking. - The unstained area in the centre of the filter can be used in conjunction with flavoured threads in the filter core. Such threads may be coloured, and disposed along the longitudinal axis of the core. The greatly reduced staining of the core region means that the thread does not become obscured during smoking of the cigarette. The external diameter of the holes can be varied as is known with current online ventilation methods to provide a wide range of ventilation levels with a wide range of hole numbers. The diameter of deep ventilation holes is typically between 0.25mm and 0.01mm, preferably between 0.2mm and 0.15mm. Ventilation levels of 10% - 80% can easily be achieved with anything from 6 to 80 holes. Obviously to achieve a given level of ventilation, where few holes are used the external diameters of the holes will be greater, and vice-versa.

For a given level of ventilation the external hole diameters are smaller than the comparable hole diameter for standard depth holes, which has the effect of reducing smoke bleed from the ventilation holes. The ventilation holes may have a depth that is at least 25% of the diameter of the filter, alternatively the depth is at least 50%, preferably the depth is at least 75% of the diameter of the filter. The ventilation holes may have a depth that is 25 - 50 % of the diameter of the filter. In real terms the ventilation holes may penetrate at least 2mm into the filter, preferably the ventilation holes penetrate 2.5mm. Optionally, the ventilation holes penetrate 3mm, or alternatively 3.5mm. Most preferably the ventilation holes penetrate 2 to 3.5mm into the filter.

Table 1 below gives a comparison of standard and deep ventilation holes.

Deep ventilation holes according to the present invention can be made by any convenient technique. In particular, the existing method of making shallow ventilation holes using a focused laser beam may be readily adapted for the fabrication of deep holes, by changing the parameters of the beam. This is particularly attractive in that existing on-line or on-machine-line laser systems can be modified for filter and cigarette manufacture in accordance with the invention.

The use of a laser to create the deep holes is also a convenient technique for forming holes with a varying permeability to provide preferential air flow in the centre of the filter. Appropriate selection of the laser operating parameters will give a beam that burns into the acetate material of the filter core in such a way that the heat generated causes the material around the hole to form a less permeable barrier in the upper part of the hole than in the deeper part, in the central region of the core.

Deep ventilation holes can be provided anywhere along the length of the filter, to engineer the filtering and dilution as desired. The filter may be a single component filter, in which the core is comprised of a single piece of core material along its entire length. Alternatively, the filter may be multi-segment filter, in which two, three or more filter components or elements are arranged in sequence along the length of the filter. The components are made from different filter materials, such as plain acetate tow, and acetate tow containing particles of carbon, each offering different filtering properties. Deep holes can be located along the filter with respect to the positions of the various segments, so that the smoke and air flow can be directed through the central or peripheral parts of the individual segments to tailor the overall filtering effect.

Similarly, deep ventilation holes can be usefully combined with annular filters.

These are filters that comprise a central portion of one filter material that is surrounded by an annular portion of another filter material. Deep holes can be used to direct the diluting air into the central portion, so that the smoke is confined to the annular portion.

Annular and multi-segment filter configurations can be used together in combination with deep ventilation holes, if one or more of the longitudinal segments in a multi-segment filter has an annular structure. This offers a wide variety of possible filter component and flow path combinations so that filtration can be engineered to achieve many different effects.

The ventilation holes can be arranged in a single row around the filter, or in a zone comprising two or more closely spaced rows. The number of holes in the row or zone, and the spacing between the holes, can be selected to give the desired level of ventilation. For example, a row or zone of thirty holes may be regarded as giving a relatively high level of ventilation. Further, deep holes of varying depth may be combined in a single row or zone, possibly further combined with conventional shallow ventilation holes. The examples shown in Figures 2A and 2B and described above are cigarettes of a simple construction, in which the filter has a paper wrapper surrounding its acetate core, which is in turn surrounded by a tipping paper that holds the filter and the tobacco rod together. Other cigarettes and smoldng articles to which the present invention may be applied may have more complex constructions, in particular with regard to the various papers and wrappers surrounding the filter core. For example, multi-segment filters may comprise several layers of paper used to wrap and connect the various segments. For the puiposes of the invention, however, the term "wrapper" when applied to the filter is intended to include single or multiple layers of wrapping around the core, and applies both to the filter wrapping layers alone if the holes are fabricated in the filter before the smoking article is assembled, and to the filter wrapping plus the tipping paper if the holes are fabricated after the smoking article is assembled. The deep ventilation holes extend through the wrapper and into the core material of the filter regardless of the number of layers that make up the wrapper. The deep ventilation holes in the filter may be formed before or after the incorporation of the filter into the smoking article. In the case of deep ventilation holes being formed in the filters of assembled smoking articles, the laser that is used to form the deep ventilation holes may be operated in situ on the machine assembling the smoking articles.

Claims

1. A filter for a smoking article comprising: a core; a wrapper surrounding the core; and at least one ventilation hole extending though the wrapper into the core to a depth such that air drawn in through the ventilation hole enters a central region of the core.

2. A filter according to claim 1, in which the ventilation hole is configured such that air drawn in through the ventilation hole preferentially enters the central region of the core.

3. A filter according to claim 2, in which the ventilation hole is defined by a surface that is more permeable to air in the central region of the core than in a peripheral region of the core.

4. A filter according to any one of claims 1 to 3, in which the ventilation hole has a depth of at least 2 mm.

5. A filter according to any one of claims 1 to 3, in which the ventilation hole has a depth in the range of 2 - 3.5 mm.

6. A filter according to any one of claims 1 to 5, in which the ventilation hole has a depth that is at least 25% of the diameter of the filter.

7. A filter according to any one of claims 1 to 5, in which the ventilation hole has a depth in the range of 25 - 50 % of the diameter of the filter.

8. A filter according to any preceding claim, comprising a plurality of the said ventilation holes.

9. A filter according to claim 8, in which the plurality of ventilation holes are arranged in at least one circumferential row or zone around the filter.

10. A filter according to any preceding claim, in which the filter is a multi-segment filter such that the core comprises two or more segments disposed longitudinally along the filter.

11. A filter according to any preceding claim, in which the filter is an annular filter such that at least part of the core comprises a central portion surrounded by an annular portion.

12. A filter according to any preceding claim, further comprising a flavour thread disposed longitudinally in the central region of the core.

13. A filter according to any preceding claim, in which the wrapper is permeable to at least one gas carried by smoke from burning tobacco.

14. A filter according to claim 13, in which the wrapper is permeable to carbon monoxide.

15. A filter according to any preceding claim, in which the ventilation hole or holes are made using a laser beam.

16. A smoking article comprising a filter according to any preceding claim.

17. A filter for a smoking article substantially as described herein with reference to Figures 2 A, 2B, 2C and 2D of the accompanying drawings.

18. A smoking article substantially as described herein with reference to Figures 2 A, 2B, 2C and 2D of the accompanying drawings.

19. A method of manufacturing a filter for a smoking article, the filter comprising a core and a wrapper surrounding the core, the method including forming at least one ventilation hole which extends though the wrapper into the core to a depth such that air drawn in through the ventilation hole enters a central region of the core.

20. A method according to claim 19, including configuring the ventilation hole such that air drawn in through the ventilation hole preferentially enters the central region of the core.

21. A method according to claim 20, including configuring the surface of the ventilation hole such that the surface is more permeable to air in the central region of the core than in a peripheral region of the core.

22. A method according to any one of claims 19 to 21, including configuring the ventilation hole to have a depth of at least 2 mm.

23. A method according to any one of claims 19 to 21, including configuring the ventilation hole to have a depth in the range of 2 - 3.5 mm.

24. A method according to any one of claims 19 to 23, including configuring the ventilation hole to have a depth that is at least 25% of the diameter of the filter.

25. A method according to any one of claims 19 to 23, including configuring the ventilation hole to have a depth in the range of 25 - 50 % of the diameter of the filter.

26. A method according to any one of claims 19 to 25, including generating a plurality of the said ventilation holes.

28. A method according to claim 26, including arranging the plurality of ventilation holes in at least one circumferential row or zone around the filter.

29. A method according to any one of claims 19 to 28, including configuring the filter in the form of a multi-segment filter such that the core comprises two or more segments disposed longitudinally along the filter.

30. A method according to any one of claims 19 to 29, including configuring the filter in the form of an annular filter such that at least part of the core comprises a central portion surrounded by an annular portion.

31. A method according to any one of claims 19 to 30, including configuring the filter to comprise a flavour thread disposed longitudinally in the central region of the core.

32. A method according to any one of claims 19 to 31, in which the wrapper is permeable to at least one gas carried by smoke from burning tobacco.

33. A method according to claim 32, in which the gas is carbon monoxide.

34. A method according to any one of claims 19 to 33, including using a laser beam to form the ventilation hole or holes.

35. A method according to claim 34, including operating the laser in situ on a machine for manufacturing smoking articles provided with the filter.

36. A method of manufacturing a smoldng article comprising a filter according to any one of claims 1 to 17.